1. Field of the Invention
The present invention relates to a magnetic recording and reproducing apparatus, and more specifically to an apparatus for recording and reproducing video signals, audio signals, computer data, etc. on and from a magnetic tape digitally, while keeping an upper compatibility with another magnetic recording and reproducing apparatus of helical scanning type designed in conformity with the well-known VHS standard, S-VHS standard, etc.
2. Description of the Related Art
An example of related art magnetic recording and reproducing apparatus of helical scanning type will be explained hereinbelow with reference to FIG. 1 to FIG. 5. FIG. 1 is a plane view showing the same related art apparatus; FIG. 2(A) is a plane view showing a rotary drum of the related art same apparatus, on which first to third magnetic heads are mounted; FIG. 2(B) is a front view of the same rotary drum; FIG. 2(C) is a view showing the mounting heights of both the first and second magnetic heads; FIG. 3 is a view showing the status where a video signal pattern, a high fidelity audio (Hi-Fi FM audio) signal pattern, and a control pulse are recorded on a magnetic tape, by use of the related art magnetic recording and reproducing apparatus of helical scanning type; FIG. 4 is an enlarged plane view showing the vicinity of the rotary drum for assistance in explaining an X value shown in FIG. 3; and FIG. 5 is a structural view (block diagram) showing a related art control pulse recording section for recording the control pulse on the magnetic tape by use of the same related art magnetic recording apparatus of helical scanning type.
As shown in FIG. 1, in the related art magnetic recording and reproducing apparatus 1A of helical scanning type designed in conformity with the well-known VHS standard, S-VHS standard, etc., a magnetic tape 4 is pulled out of a tape cassette 3 mounted on a chassis base 2, and further wound helically around a fixed drum 5 fixedly mounted on a chassis base 2 and around a rotary drum 6 rotatably mounted coaxially with the fixed drum 5 over a predetermined angle, so that signals can be recorded and reproduced on and from the magnetic tape by use of first, second and third magnetic heads 7 to 9 mounted on the rotary drum 6 integral therewith. Further, the control pulse is recorded on a lower side edge portion of the magnetic tape 4 by use of a control head 10a of an AC (audio control) head 10 fixedly mounted on the downstream side of the rotary drum 6. Further, when the control pulse is reproduced, the travel of the magnetic tape 4 pinched between a capstan 11 and a pinch roller 12 can be controlled on the basis of the control pulse.
Here, the fixed drum 5 is formed with a lead (not shown) for guiding the lower side edge portion of the magnetic tape 4 helically at a predetermined lead angle. Further, a predetermined angle over which the magnetic tape 4 is wound around the rotary drum 6 is defined by a tape wound-up angle between an inlet position (i.e., reference angle 0.degree.) at which the magnetic tape 4 begins to contact with the outer circumference surface 6a of the rotary drum 6) and an outlet position at which the magnetic tape 4 begins to be separated from the outer circumference surface 6a of the rotary drum 6. Further, in order to secure the compatibility with the other magnetic tapes 4 in accordance with the well-known VHS standard and S-VHS standard, in the case of a large diameter (about 62 mm) rotary drum 6, the tape wound-up angle is set to roughly 180.degree.; on the other hand, in the case of a small diameter (about 41.3 mm) rotary drum 6, the tape wound-up angle is set to roughly 270.degree..
Here, when the drum diameter of the rotary drum 6 is large (e.g., about 62 mm), for instance as shown in FIG. 2(A), the first magnetic head 7 mounted on the rotary drum 6 integral therewith is composed of a pair of the first magnetic heads 7a and 7b having two different azimuth angles of .+-.6.degree. in correspondence to 1ch and 2ch so as to record and reproduce video signals in standard time mode; the second magnetic head 8 mounted on the same rotary drum 6 is composed of a pair of the second magnetic heads 8a and 8b having two different azimuth angles of .+-.30.degree. in correspondence to 1ch and 2ch so as to record and reproduce high fidelity audio (Hi-Fi FM audio) signals in standard play (ST) time and long play (LP) time modes; and the third magnetic head 9 mounted on the same rotary drum 6 is composed of a pair of the third magnetic heads 9a and 9b having two different azimuth angles of .+-.6.degree. in correspondence to 1ch and 2ch so as to record and reproduce video signals in long time mode. These magnetic heads are all arranged along the outer circumferential surface 6a of the rotary drum 6 being separated from each other by a predetermined angle, respectively in such a way that each pair (7a and 7b), (8a and 8b) or (9a and 9b) of the first to third magnetic heads 7 to 9 is mounted in 180.degree. symmetrical positional relationship with respect to each other with an axle 6b of the rotary drum 6 as its center.
Further, the 1ch second magnetic head 8a is mounted on the rearward side by 42.degree. from the 1ch first magnetic head 7a; the 2ch second magnetic head 8b is mounted on the frontward side by 138.degree. from the 1ch first magnetic head 7a; and the 1ch second magnetic head 8a is mounted on the frontward side by 138.degree. from the 2ch first magnetic head 7b. Further, the 1ch third magnetic head 9a is mounted on the frontward side from the 1ch first magnetic head 7a; and the 2ch third magnetic head 9b is mounted on the frontward side from the 2ch first magnetic head 7b.
Further, as shown in FIG. 2(B), the first magnetic heads 7a and 7b and the third magnetic heads 9a and 9b are mounted on the bottom surface 6c of the rotary drum 6. On the other hand, the second magnetic heads 8a and 8b are mounted at a high position a distance d (e.g., about 63 .mu.m) higher than the bottom surface 6c of the rotary drum 6.
Further, for convenience of explanation, the description is omitted herein of the VHS standard for recording and reproducing video signals by use of the first magnetic heads 7a and 7b or the third magnetic heads 9a and 9b and for recording and reproducing audio signals by use of an audio head 10b of the AC (audio control) head 10.
Further, the related art magnetic recording and reproducing apparatus 1A constructed as described above adopts such a deep layer recording method that high fidelity audio signals are recorded in a deep magnetic layer portion of the magnetic tape 4 by use of the second magnetic heads 8a and 8b and further, after the high fidelity audio signals have been recorded, video signals are recorded on a surface magnetic layer portion of the same magnetic tape 4 by use of the first magnetic heads 7a and 7b or the third magnetic heads 9a and 9b. This deep layer recording method is applied to the well-known VHS and S-VHS standards.
In the above-mentioned deep layer recording method, in general, the 1ch first magnetic head 7a and the 2ch second magnetic head 8b are used as one set, and the 2ch first magnetic head 7b and the 1ch second magnetic head 8a are used as the other set.
Therefore, when the 1ch first magnetic head 7a and the 2ch second magnetic head 8b (going ahead of the 1ch first magnetic head 7a) are paired, the positional relationship between both the magnetic heads 7a and 8b on the magnetic tape 4 can be shown as in FIG. 2(C).
In this case, as shown by FIGS. 2(B) and 2(C), although the 1ch and 2ch second magnetic heads 8a and 8b are mounted along the outer circumferential surface 6a of the rotary drum 6 at the above-mentioned predetermined mounting angles and the above-mentioned predetermined mounting height d, respectively, since the second magnetic heads 8a and 8b are only required to be arranged along video signal patterns V.sub.1 and V.sub.2 (described later with reference to FIG. 3) in accordance with VHS and S-VHS standards, each maker can freely decide the mounting angles and the mounting height of the second magnetic heads 8a and 8b on the rotary drum 6, from the design standpoint.
Therefore, as shown in FIG. 3, when video signals and high fidelity audio signals are recorded in analog fashion at a predetermined inclination angle with respect to the longitudinal direction of the magnetic tape 4 in conformity with the well-known S-VHS standard, after the analog high fidelity audio signal pattern HA.sub.2 has been deep-recorded narrowly on the deep magnetic layer portion of the magnetic tape 4 by use of the 2ch second magnetic head 8b (going ahead of the 1ch first magnetic head 7a), the analog video signal pattern V.sub.1 is superpose-recorded widely than the high fidelity audio signal pattern HA.sub.2 on the surface magnetic layer portion of the magnetic tape 4 by use of the 1ch first magnetic head 7a. In the same way, after the high fidelity audio signal pattern HA.sub.1 has been recorded by use of the 1ch second magnetic head 8a (going ahead of the 2ch first magnetic head 7b), the video signal pattern V.sub.2 is recorded by use of the 2ch first magnetic head 7b, the above-mentioned sequence being repeated.
Further, on the lower side edge portion of the magnetic tape 4, the control pulse C is recorded by use of the control head 10a via control pulse recording means 20 (described later with reference to FIG. 5).
Here, under consideration of the compatibility with the magnetic recording and reproducing apparatus and the magnetic tape 4 designed in conformity with both the VHS standard and S-VHS standard (the same standard as with the case of the magnetic recording and reproducing apparatus 1A), as shown in FIGS. 3 and 4, a distance X [X value] is previously prescribed in accordance with the standards. Here, X value is a distance between an outlet position (the outlet position of the rotary drum 6) at which the 2ch first magnetic head 7b reaches the outlet position of the video signal pattern V.sub.2 and the control head 10a on the magnetic tape 4. Further, when the 2ch first magnetic head 7b reaches the outlet position of the video signal pattern V.sub.2 (the outlet position of the rotary drum 6), the control pulse C is recorded on the magnetic tape 4 by use of the control head 10a.
In more detail, as shown in FIG. 5, control pulse recording means 20 for recording the control pulse on the magnetic tape 4 by use of the control head 10a is composed of a control pulse forming circuit 21 for outputting the control pulse of 30 Hz as one-frame reference of the video signals, whenever the 2ch first magnetic head 7b reaches the outlet position of the video signal pattern V.sub.2 (the outlet position of the rotary drum 6); a recording amplifier 22 for amplifying the control pulse formed by the control pulse forming circuit 21; and the control head 10a for recording the control pulse amplified by the recording amplifier 22 on the lower side edge portion of the magnetic tape 4 at a predetermined position on the magnetic tape 4, that is, a distance of the X value away from the position at which the 2ch first magnetic head 7b reaches the outlet position of the video signal pattern V.sub.2 (the outlet position of the rotary drum 6).
Therefore, when the magnetic tape 4 is driven at a speed V (mm/sec), there exists a time difference X/V (sec) between the outlet position at which the 2ch first magnetic head 7b reaches the outlet position of the video signal pattern V.sub.2 (the outlet position of the rotary drum 6) and the position at which the control pulse C is recorded (on the basis of conversion from distance to time).
Further, the above-mentioned X value can secure the compatibility between the apparatus 1A and the magnetic tapes 4, by deciding the timing at which the control pulse is recorded by use of the control head 10a, in relation to the video signal patterns V.sub.1 and V.sub.2 recorded on the magnetic tape 4 by the 1ch and 2ch first magnetic heads 7a and 7b, respectively.
Further, in the above-mentioned magnetic recording and reproducing apparatus 1A, although the operation of reproducing the signals recorded on the magnetic tape is not described, it is obvious that the travel of the magnetic tape is controlled on the basis of the control pulse recorded as described above.
By the way, although the above-mentioned magnetic recording and reproducing apparatus 1A designed in conformity with the well-known S-VHS standard is widely used, in the case of the deep-layer recording method, the video signals are recorded on the surface magnetic layer portion of the magnetic tape 4 in analog fashion and further the high fidelity audio signals are recorded on the deep magnetic layer portion of the magnetic tape 4 also in analog fashion.
On the other hand, although many magnetic recording and reproducing apparatus for recording and reproducing video signals, audio signals, computer data, etc. on and from the magnetic tape in digital fashion have been developed, in the case of the digital magnetic recording and reproducing apparatus, since there exists no compatibility with the analog magnetic recording and reproducing apparatus, it is impossible to reproduce the signals recorded on the magnetic tape 4 in analog fashion.
To overcome this problem, the same Applicant has proposed a magnetic recording and reproducing apparatus designed in conformity with D-VHS standard, for recording and reproducing video signals, audio signals, computer data, etc. on and from a magnetic tape in digital fashion, while keeping an upper compatibility with another analog magnetic recording and reproducing apparatus of helical scanning type designed in conformity with the well-known VHS standard and S-VHS standard.
Here, in the proposed magnetic recording and reproducing apparatus, video signals, audio signals and computer data can be recorded and reproduced on and from the magnetic tape 4 in digital fashion, by use of only the above-mentioned 1ch and 2ch second magnetic heads 8a and 8b.
In this case, when the timing at which the control pulse is recorded by use of the control head 10a is set in relation to the signal pattern recorded by use of the 1ch and 2ch second magnetic heads 8a and 8b in digital fashion, if the X value prescribed in accordance with the VHS standard and the S-VHS standard is used as it is, the following problem arises:
In more detail, if the start position at which the control pulse is started to be recorded on the side edge portion of the magnetic tape 4 by use of the control head 10a is set to the X value in correspondence to the time point when the 2ch second magnetic head 8b reaches the outlet position of the rotary drum 6, since the mounting angles and the mounting height d of both the 1ch and 2ch second magnetic heads 8a and 8b are decided unconditionally, there exists a problem in that such condition that the mounting angles and the mounting height d of the 1ch and 2ch second magnetic heads 8a and 8b cannot be set freely according to each maker as already explained. As a result, there exists a need of solving the above-mentioned problem involved in the related art magnetic recording and reproducing apparatus.
In addition, when the apparatus size is required to be reduced, since there exists the case where the mounting position of the control head 10a cannot be decided at the above-mentioned X value position, the magnetic recording and reproducing apparatus which can satisfy the compatibility in this point of view is desired.